One phenomenon which has a negative effect on the reliability of rolling bearings are white etching cracks or WECs (the term used predominantly among technical experts even those who are German speakers). White etching cracks are changes in the microstructure of the material which form below the bearing surface. These can propagate as far as the surface under the influence of various external loads. As a result, pits or flaked areas may form and fracture of the inner or outer ring and thus premature failure of the bearing concerned may even occur. White etching cracks occur both in fully hardened and in case-hardened rolling bearings. The reasons for the formation of white etching cracks have not yet been fully explained. However, according to the current state of knowledge, additional stresses in the form of dynamic loads and/or hybrid friction and/or electrical phenomena are preconditions for the formation of white etching cracks. In particular, increased hydrogen absorption into the boundary layer of the material at the point of rolling contact is regarded as a fundamental cause of the formation of white etching cracks. Hydrogen formation and absorption are caused by the additional stress due, for example, to high frictional stress in the rolling surfaces and/or due to additional electric loads. Such white etching cracks are described in EP 2 573 195 A1, for example.
To increase resistance to white etching cracks in a rolling bearing, EP 2 573 195 A1 proposes the provision of a compound layer on the bearing surface of the rolling bearing. In this case, the compound layer has a lower yield stress than the remainder of the material of the rolling bearing. This is accomplished by heating the rolling bearing at a certain temperature for a certain time and bringing the bearing surface into contact with a chemical additive.